Process and plant for hardening glass plates

ABSTRACT

A system for tempering glass plates has preheating zone (1) in which several glass plates (7) stacked vertically in compartmented car (6) are heated together to a temperature below the tempering temperature of for example 650° C. (for example 300° C.). Preheated glass plates (7) are moved individually from preheating zone (1) into heating zone (2). In heating zone (2) glass plates (7) are heated to the tempering temperature, their being inclined to the vertical at an acute angle and being held by air cushions between two heating plates. On the lower edge of the two heating plates of heating zone (2) there is transport device which supports glass plates (7) simultaneously to the bottom. Glass plates (7) heated to the tempering temperature are moved into cooling zone (3) which has cooling plates aligned parallel to the heating plates and between which glass plate (7) is pushed for quenching. The cooling plates can also be placed on the two sides of glass plate (7) to be tempered for purposes of quenching. The quenched glass plates which still have a temperature of for example 300° C., are transported into after-cooling zone (4) in which they are slowly cooled to room temperature after being deposited in compartmented cars (6). 
     Because glass plates (7) are placed in heating zone (2) and cooling zone (3) obliquely, not horizontally, there are no problems with support and transport of glass plates (7). Joint preheating of glass plates (7) and joint cooling of glass plates (7) to room temperature after quenching thereof save considerable energy since the heating and cooling power in preheating zone (1) and aftercooling zone (4) can be low.

The invention relates to a process with the feature of the introductorypart of the preamble of claim 1.

The invention furthermore relates to a system (device) with the featuresof the introductory part of the independent apparatus claim.

Glass plates are tempered by heating them to a temperature ("temperingtemperature") above 650° C. and then quenching them at a temperaturewhich is below the critical temperature, for example less than 300° C.,so that stresses which temper the glass form due to the shock cooling.

In the known devices the cost for heating the glass plates and thequenching costs thereof are very high. In particular in the knowndevices considerable amounts of energy are needed for operating the fanwhich delivers the heated gases for heating the glass plates.

The object of the invention is to improve glass tempering and thesystems provided for this purposes such that the cost in energy and timeis reduced and good glass tempering is still achieved.

As claimed in the invention this object is achieved with the features ofthe main process claim. With regard to the proposed system (device) asclaimed in the invention the object is achieved with the features of theindependent main apparatus claim.

Because in the invention glass plates are preheated for example togetherand then heated to the required tempering temperature preferablyindividually and furthermore quenching to a temperature below thecritical temperature is done preferably individually and the glassplates are then cooled for example together to room temperature, largeamounts of time and energy are saved, since the heating and coolingzones need only be short. The invention is based on the finding that itis enough for tempering of glass plates if the temperature jump from thetempering temperature, for example of 650° C., to a temperature belowthe critical temperature, for example, roughly 300° C., takes placequickly to achieve the desired tempering effect. Preheating and coolingto room temperature can then be done slowly without any adverse effecton the tempering of the glass plates. The adverse, nonuniform surfacestresses which lead to undulations in the glass plates and which form inthe known processes are avoided.

Other details and features of the invention result from the followingdescription of the glass plate tempering system shown by way of examplein the drawings.

FIG. 1 shows the overall system in an oblique view;

FIG. 2 shows the heating and quenching zone in a larger view; and

FIG. 3 shows two heating zones and one quenching zone.

The system as claimed in the invention which is shown in FIG. 1 consistsof four zones, specifically preheating zone 1, heating zone 2, coolingzone 3 and after-cooling zone 4.

In preheating zone 1 which is housed in closed chamber 5, glass plates 7standing in shelves, for example compartmented cars 6, are preheatedtogether and heated for example to a temperature of roughly 300° C.Compartmented cars 6 used in preheating zone 1 can have a constructionas they are known from EP 603 151 A or EP 704 389 A. Only the bottom andside rollers or sleeve-shaped slide parts of compartmented cars 6 aremade of a correspondingly temperature resistant material due to the hightemperature stress.

As shown in FIG. 1, compartmented cars 6 are guided to move on rails 8transversely to the alignment of the compartments which hold glassplates 7 and which are provided in the cars so that a selected preheatedglass plate 7 can be delivered to tilt table 9, from which it isconveyed with the inclined position which corresponds to heating zone 2from preheating chamber 5 to heating zone 2. Tilt table 9 isadvantageously made with a support surface executed as an air cushionwall.

According to one embodiment, between preheating chamber 5 in which glassplates 7 are jointly preheated, and heating zone 2 in which glass plates7 are heated individually for example to a temperature of 650° C., therecan be another heating zone 27 in which glass plates 7 are heatedindividually to a temperature between the temperature in preheatingchamber 5 and that of heating zone 2. This embodiment is shown in FIG 3.

One advantage of preheating chamber 5 in which several glass plates 7are heated together is that the heating can take place accordinglyslowly and thus with low energy consumption, since there is enough timefor preheating. Thus in the embodiment it is shown that in chamber 5there are several, for example, two compartmented cars 6 and thatcompartmented car 6 loaded with glass plates 7 and moved last intopreheating chamber 5 is only moved into the removal point provided nextto tilt table 9 when compartmented cars 6 located at the removal pointhave been emptied. Then new compartmented car 6 filled with glass plates7 is moved into the waiting zone of preheating chamber 5 and glassplates 7 located in it are slowly heated up.

Heating zone 2 is shown in FIG. 2 in more detail. In contrast to knownheating zones for heating of glass plates in their tempering heatingzone 2 as claimed in the invention is aligned such that glass plates 7are aligned, not horizontally, but tilted almost to vertical. To do thisheating zone 2 (like cooling zone 3 downstream of it) is aligned withtilt adjustment 11, for example in the form of pneumatic or hydrauliccylinders, so that the tilt of heating zone 2 or glass plates 7 locatedin it can be adjusted according to requirements (size and thickness ofthe glass plate). In this way the problems in transport and support ofglass plates (deformation/sagging) which occur in heating zones withhorizonal glass plates are prevented.

For support on the lower edge of glass plate 7 there is transport device12 which, as shown in the embodiment, can be a continuous transportbelt, but there can also be a transport device which is made inprinciple as is described in DE 30 38 425 A, in which the horizontalsupport of the conveyor means can reach in full or in part under glassplates 7 on their lower edge. Preferably the supports which reach underglass plates 7, especially when they reach under the glass plates intheir entirety, are attached offset to one another to opposing chains orother continuous conveyor elements.

In the embodiment shown heating zone 2 has two opposite heating plates15 which leave a space between themselves for glass plates 7 to beheated and which can be heated in any manner. For example the heatingsystem can be an electrical heating system or gas heating system.

In heating plates 15 which can have a surface made to increase andsupport emission of heat radiation there is a series of holes 16 whichcan be loaded with pressurized gas via chamber 17 so that on both sidesof glass plate 7 located between heating plates 15, gas cushions,especially air cushions, form. Thus, glass plate 7 touches neither oneor the other heating plate 15, but is merely supported and transportedon its lower edge by transport means 12.

One embodiment of heating plates 15 is conceivable in which heatingplate 15 located above glass plates 7 has no holes 16 so that heat isreleased for the most part by heat radiation from upper heating plate 15onto glass plate 7 to be heated.

In the invention, heating zone 2 can therefore be made such that fromlower heating plate 15 heat is released onto the glass plate primarilyby radiation and convection, from upper glass plate 15 primarily byradiation.

To deliver gas to heating plates 15 to form the air cushion, anappropriately preheated compressed gas, for example, air, can besupplied to chambers 17. But it is also possible to form the air cushionby combustion gases which are formed in the burning of gas, thecombustion heat being used at the same time to heat up heating plates15.

To adapt to different glass plate sizes, heating plates 15 can bedivided into sections which extend for example parallel to transportdevice 12, therefore to the conveyance direction, and which, dependingon the length of glass plate 7 measured away from transport device 12,can be started or stopped. This saves even more energy.

Heating plates 15 are also built into the device in a manner not shown,such that the distance of heating plates 15 from one another can bechanged to adapt to the thickness of the glass plate to be tempered. Indoing so it is enough if upper heating plate 15 is adjustable, forexample, by hydraulic cylinders or similar servo drives, relative tolower heating plate 15.

Because heating zone 2 is formed as claimed in the invention glass plate7 is for example rapidly heated from the preheating temperature of 300°C. to the tempering temperature of for example 650° C. primarily byradiation, supported by convection.

Adjacent to heating zone 2 there is cooling zone 3 which is madeidentical to heating zone 2 in terms of construction, and in it thereare cooling plates 20, through which for example a cooling medium flows(not shown). Exit holes 16 in two cooling plates 20 are loaded with acorrespondingly cooled gas so that air cushions, now cooling, describedbeforehand in conjunction with heating zone 2, form, and they arelocated above and below glass plate 7 to be quenched, or only underglass plate 7.

Cooling plates 20 are likewise made to move relative to one another sothat they can be brought closer to one another or moved farther apart.This can also be used to place cooling plates 20 briefly on bothsurfaces of glass plate 7 while the air cushion is turned off andtransport 12 is shut down in order to accelerate quenching for purposesof tempering of glass plate 7. This approach is used preferably in thinglass plates 7. For thicker glass plates 7 it is often advantageous todeliver cold air to glass plates 7 to be quenched, generally from bothsides, and to stop glass plates 7 in the area of cooling zone 3.

When cooling plates 20 are placed on glass plate 7, transport 12 in thearea of cooling zone 2 is shut down to prevent undesirable relativemotion between glass plate 7 and transport 12.

It should be pointed out that transport 12 can also be shut down in thearea of heating zone 2 if for example glass plates 7 are so large and/orthick that they cannot be heated to the required tempering temperaturein continuous operation.

Following cooling zone 3, glass plates 7 via tilt table 25 reachaftercooling zone 4 which can be housed in a chamber and which likewisecontains compartmented cars 6 of the aforementioned type, in which glassplates 7 can be deposited sorted by consignments into compartmented cars6, to then be cooled to room temperature. Here the cooling power neednot be great since there is enough time for cooling. Otherwise it ispossible, when aftercooling zone 4 is housed in one chamber (see thechamber in FIG. 1 illustrated with a broken line), to deliver heated airfrom aftercooling zone 4 into preheating zone 1 to save energy (pipeline26).

The surfaces of cooling plates 20 facing glass plates 7 can be made tosupport the absorption of heat radiation. For example, the surfaces ofcooling plates 20 facing one another can be made ribbed or rippled toincrease the area of cooling plates 20 which absorbs heat.

In the system as claimed in the invention glass plates 7 are moved, notlying horizontally, but inclined to the vertical, for example at anacute angle, through heating zone 2 and downstream cooling zone 3 sothat in the system as claimed in the invention the former problems inconjunction with supporting glass plates 7 and their transport whichhave often led to deformations of glass plates 7 do not arise.

By means of transport devices 12 which engage the lower edge of glassplates 7 the latter can be moved with the desired speed through heatingzone 2 and cooling zone 3, it being easily possible to stop glass plates7 if necessary in heating zone 2 and/or cooling zone 3 for a short time;this is of special interest when in cooling zone 3 cooling plates 20 areto be placed from both sides on glass plate 7 to be quenched.

Thus, like heating plates 15, cooling plates 20 can also be divided intovarious zones so that the area of cooling plates 20 which is active forcooling can be matched to the size of glass plate 7 to be quenched (itslongitudinal extension measured away from the conveyor means).

To avoid the need to continuously turn the different zones of heatingplates 15 and/or cooling plates 20 on and off, it is possible to proceedsuch that glass plates 7 with an identical height or one as similar aspossible can be removed from preheating zone 1 and sent in successionthrough heating zone 2 and cooling zone 3. Tempered glass plates 7 canbe sorted again by consignments in aftercooling zone 4.

In summary, one embodiment of the invention can be described as follows.

A system for tempering glass plates has preheating zone 1 in whichseveral glass plates 7 stacked vertically in compartmented car 6 areheated together to a temperature below the tempering temperature of forexample 650° C. (for example 300° C.) Preheated glass plates 7 are movedindividually from preheating zone 1 into heating zone 2. In heating zone2 glass plates 7 are heated to the tempering temperature, their beinginclined to the vertical at an acute angle and being held by aircushions between two heating plates. On the lower edge of the twoheating plates of heating zone 2 there is transport device whichsupports glass plates 7 simultaneously to the bottom. Glass plates 7heated to the tempering temperature are moved into cooling zone 3 whichhas cooling plates aligned parallel to the heating plates and betweenwhich glass plate 7 is pushed for quenching. The cooling plates can alsobe placed on the two sides of glass plate 7 to be tempered for purposesof quenching. The quenched glass plates which still have a temperatureof for example 300° C., are transported into aftercooling zone 4 inwhich they are slowly cooled to room temperature after being depositedin compartmented cars 6.

Because glass plates 7 are placed in heating zone 2 and cooling zone 3obliquely, not horizontally, there are no problems with support andtransport of glass plates 7. Joint preheating of glass plates 7 andjoint cooling of glass plates 7 to room temperature after quenchingthereof save considerable energy since the heating and cooling power inpreheating zone 1 and aftercooling zone 4 can be low.

We claim:
 1. Process for tempering of glass plates in which glass platesare heated to a temperature above the tempering temperature and cooledto a temperature below a critical temperature for tempering, wherein aplurality of the glass plates are simultaneously preheated to atemperature near the critical temperature, that the glass platespreheated in this way are individually heated to a temperature above thetempering temperature so that only one of the glass plates is heated atone time, that the glass plates are individually quenched to atemperature below the critical temperature so that only one of the glassplates is quenched at one time, and that a plurality of the glass platesare then simultaneously cooled to room temperature.
 2. Process asclaimed in claim 1, wherein the glass plates are aligned at an acuteangle to the vertical when individually heated to a temperature abovethe tempering temperature and when individually quenched to atemperature below the critical temperature.
 3. Process as claimed inclaim 1, wherein when individually heated and individually quenched theglass plates are supported in a heating zone and a cooling zone borderedby heating plates and cooling plates respectively at least fromunderneath by compressed gas cushions and are supported and transportedon their horizontal edge.
 4. Process as claimed in claim 1, wherein theglass plates for tempering are heated to a temperature above 650° C. 5.Process as claimed in claim 1, wherein the glass plates during temperingare quenched to a temperature below 300° C.
 6. Process as claimed inclaim 1, wherein the glass plates before heating are preheated to atemperature of 300° C.
 7. Process as claimed in claim 3, wherein the gaspressure cushion is formed in the area of the heating zone by heated airor combustion gases.
 8. Process as claimed in claim 3, wherein the gaspressure cushion is formed in the area of the cooling zone by cooledair.
 9. Process as claimed in claim 3, wherein the cooling platesbordering the cooling zone are placed on the glass plate from both sidesto quench it.
 10. Process as claimed in claim 3, wherein the glassplates are transported through the heating zone and/or cooling zone at aspeed matched to their thickness and optionally stopped temporarily inthe heating zone or cooling zone.
 11. Process as claimed in claim 1,wherein hot exhaust air from the aftercooling zone is used for heatingin the preheating zone.
 12. Process as claimed in claim 3, whereinheating in the heating zone takes place preferably by convection causedby the compressed gas and by radiation.
 13. Device for executing theprocess as claimed in claim 1, comprising a heating zone (2) and coolingzone (3) downstream from the heating zone, in which there are heatingplates (15) or cooling plates (20) which are at a distance from oneanother and which lie at an acute angle to the vertical, and wherein infront of the heating zone (2) there is a preheating zone (1) and afterthe cooling zone (3) there is an aftercooling zone (4);wherein thepreheating zone and the aftercooling zone are structured and arranged tocontain a plurality of the glass plates simultaneously, and wherein theheating and cooling zones are structured and arranged to contain onlyone said glass plate at one time.
 14. Device as claimed in claim 13,wherein the mutual distance of heating plates (15) in heating zone (2)and the mutual distance of cooling plates (20) in cooling zone (3) canbe changed.
 15. Device as claimed in claim 13, wherein on the lower edgeof heating plates (15) and on the lower edge of cooling plates (20)there is transport device (12).
 16. Device as claimed in claim 13,wherein the incline of heating plates (15) and cooling plates (20) tothe vertical can be changed.
 17. Device as claimed in claim 13, whereinpreheating zone (1) comprises preheating chamber (5), and wherein inpreheating chamber (5) there are shelves (6) for holding several glassplates (7) to be preheated at the same time.
 18. Device as claimed inclaim 13, wherein aftercooling zone (4) optionally comprises anaftercooling chamber and wherein in aftercooling zone (4) there areshelves (6) for holding several glass plates (7) to be cooled at thesame time.
 19. Device as claimed in claim 13, wherein at least inheating plates (15) located under glass plates (7) to be heated thereare holes (16) for exit of compressed gas for purposes of forming an aircushion between heating plate (15) and glass plate (7) to be heated. 20.Device as claimed in claim 13, wherein in cooling plate (20) locatedunder glass plate (7) to be cooled, but preferably in two cooling plates(20) in the surfaces facing glass plate (7) there are holes (16) forexit of cooled gas for forming air cushions between cooling plates (20)and glass plate (7) to be quenched.
 21. Device as claimed in claim 13,wherein heating plates (15) are equipped with electrical heating. 22.Device as claimed in claim 13, wherein heating plates (15) are heated bycombustion gases from at least one gas burner.
 23. Device as claimed inclaim 13, wherein combustion gases emerge through gas exit holes (16) inheating plates (15).
 24. Device as claimed in claim 17, wherein betweenshelves (6) for holding glass plates (7) in preheating chamber (5) andheating zone (2) there is tilt table (9) for swivelling glass plates (7)into the oblique position of heating zone (2).
 25. Device as claimed inclaim 13, wherein after cooling zone (3) there is tilt table (25) foraligning glass plates (7) from the inclined position of cooling zone (3)into the position in which they can be deposited in the compartments ofshelf (6) in aftercooling zone (4).
 26. Device as claimed in claim 17,wherein the shelves in the preheating chamber (5) and/or aftercoolingchamber (4) are made as compartmented cars (6) which can be movedtransversely to the conveyance direction.
 27. Device as claimed in claim13, wherein there is line (26) which joins the vent opening ofaftercooling chamber (4) to preheating chamber (5).
 28. Device asclaimed in claim 13, wherein heating plates (15) are divided intoseveral sections which can be heated independently of one another. 29.Device as claimed in claim 13, wherein plates (20) of cooling zone (2)are divided into several sections which can be cooled independently ofone another.
 30. Device as claimed in claim 28, wherein heating plates(15) and/or cooling plates (20) are divided into strip-shaped sectionswhich extend parallel to transport direction (12) on the lower edge ofheating zone (2) and/or cooling zone (3).
 31. Device as claimed in claim13, wherein between preheating zone (1) in which several glass plates(7) are preheated at the same time and heating zone (2) there is adevice for further heating of individual glass plates (7).